Hydraulic feeding mechanism



Uct 1951 H. ERNST ET AL HYDRAULIC FEEDING MECHANISM 2 SHEETS-SHEET 1 Filed Sept. 26, 1946 3 I muz knfiwm V333 m n O N DEE .rmzEwx DEE It z MW w mm M J Q A e. W m M w 3 N WH ct. 30, 1951 H. ERNST ET AL 25 M HYDRAULIC FEEDING MECHANISM Filed Sept. 26, 1946 2 SHEETSSHEET 2 FEED RANGE SELECTOR VALVE SHORT CIRCUITING VALVE 36d STOP VALVE I SELECTOR VALVE Patented Oct. 30., 1951 UNITED STATES PATENT OFFICE HYDRAULIC FEEDING MECHANISM Hans Ernst and Albert H. Dal], Cincinnati, Ohio, assignors to The Cincinnati Milling Machine 00., Cincinnati, Ohio, a corporation o'f Ohio Application September 26, 1946, SefiafNo. 699,424

16 Claims. 1

invention pertains to hydraulic transmission and control mechanism for machine tools and is particularly related to hydraulic feeding mechanism for millin machines.

One of the objects of this invention is to provide an improved hydraulic feeding mechanism fora milling machine.

Another object is to provide an improved hydraulic feed actuating mechanism for a milling machine slide which is responsive and automatically compensative to neutralize tentative variations in the slide movement due to the cutting force's. Still another object is to provide a hydraulic feeding system for a milling machine adapted to effect a smooth and uniform movement between work and tool regardlesso'f' variations in the cutting forces imposed on the system by the machining operation.

A still further object is to provide a dual hydraulic motor drive for actuating a machine tool member which is automatically responsive to fluctuating forces applied to said member to counteract said forces in their incipien'cy and therby maintain a uniform steady motion in said member.

Other objects and advantages of the present invention should be readily apparent by reference to the following specification, considered in conjunction with "the accompanying drawings "forming a part thereof andit is to be understood that any modifications may be made in the'exa'ct structural details there shown and described, within the scope oi the appended claims, without departing from or exceeding the spirit of the invention.

the basic principles of operation of this inven- 'tion.

Figure 2 is a hydraulic circuit diagram showwork table is moved in relation to a rotary toothed V cutter which inherentiy creates periodic ior'c'es.

The intermittentcutting action of the cutter teeth on "the work piece'and the change ineffective work resistance due to di'iierent amounts or stock to be removed at points in the cutting cycle or change indirection "of rotation of the cutter with respect to the direction of feed result in wide variations in the forces and their direction of reaction on the feed transmission actuating the table. Such action must be counterbalanced to insure the smooth motion in the Work tablewhich is so desirable for the ultimate accuracy and "high degree of finish required on the work piece.

This invention is particularly adapted to pro-'- vide an *actuatingvmeansfor the work table which is sensitive and responsive to the fluctuating loads imposed by the reaction between cutter and work so as to automatically instantly oppose and prevent changes in the rate of movement of the .work table during the cutting operation. Fig ure 1 is shown in an elementary way the basic elements *of this novel feeding mechanism and the various pressure conditions which may develop in the system under different cutting and idle operating conditions. The work table T actuated and controlled in its movements by 'a pair of hydraulic motors Ml and M2. These motors may comprise any suitable type "of hydraulic actuator but preferably are of the rotary motor type in order to minimize the volume of the hydraulic fluid necessary for their operation and thereby reduce the eife'ct of the compressibility 'ofthe actuating fluid on the desired operation of the device. Each motor is connected to the work table T by any suitable mechanical drive means such as the transmission gears in and I ljFigures 1 and '2, which are coupled with a common rack I 2 rigidly fixed to the work table hy'any suitable means [3.

A locked'hydraulic circuit is preferably utilized for energizing these motors including a variable delivery pump 14 whichffor example, supplies pressure to "the intake port f5 of the hydraulic motor Ml and withdraws fluid 'from the exhaust port [6 of this motor for one direction of movement, or vice versa for the other .direction of movement. The-second hydraulic backlash or opposer motor M2 is connected in parallel with the motor MI through a pair of automatically adjustable resistances RI and R2 respectively associated with the ports H and I8 of the motor M2.

Assuming a condition of operation in which the "table T is being fed to the left as indicated by the arrows 28 in Figure .1, and a hydraulic circuit hook-up a's s'hown at I, U ,and D inthis 5.5 figure, and'a variable-deliver pump 1 4 oneosi- 3 tive displacement type provides fluid pressure from its outlet port 30 to the ports l and ll of the motors MI and M2 which act as intake ports of these motors. The ports l6 and I8 act as discharge ports of the respective motors MI and M2 under these circumstances and connect to the intake port 29 of the pump IA. The pump I4 is adapted to positively transfer at all times a certain definite volume of fluid from its intake port 29 to its exhaust port 30 under one direction of feeding, as here illustrated when feeding in the direction 28. This positive fluid transfer is maintained independently of any pressure changes at the ports 29 and 30. Interconnected between the ports l5 and ll of the motors MI and M2 is an adjustable fluid resistance RI and between the ports l6 and iii of these respective motors is an adjustable fluid resistance R2, which are connected with the pump M in a locked or closed hydraulic circuit.

. In this elementary system various operating conditions take place, depending upon whether the table T is being fed in idle condition with no engagement of cutter and work; whether a downcutting or climb milling operation is taking place, or whether a conventional up-cut milling is being done.

Referring to the elementary circuit indicated at -I in the central portion of the diagram, Figure 1, and assuming the table feedin to the left in the direction indicated by the arrow 28 and with the elementary circuit between the variable delivery pump l4 and the motors MI and M2 arranged as described above, the only resistance to the normal direction of feeding motion at this time will be that of the friction in the feed transmission and the slideways between the table and its support in the machine. This frictional resistance is indicated in the diagram at F and represents the distance between the broken line l9, indicating no friction or work resistance, and the line 20. This frictional resistance F in effect acts as a positive work resistance during table movement, i. e., it represents a force which opposes the direction of feeding movementof the work table when being fed in idle movement with no en agement of work and cutter. This positive frictional resistance must be overcome by the driving action :of the motor Ml to effect idle movement of the :table.

In addition, in order to provide smooth non.-

-jumping operation of the work table under idle feeding movements, there is also maintained a somewhat smaller opposing force against the action of the motor Ml acting in effect as a positive work resistance opposing the direction of feeding movement during the idle feeding movement. This is provided by the second motor M2 which is connected in the elementary circuit as above explained through the adjustable resistances RI and R2 which are automatically regulated so that at the time of idle feeding, the motor M2 opposes the driving rotation of the motor Ml through the .rackl2 by maintaining a, somewhat higher fluid pressure B2 at its discharge port l8 than at its intake port ll. Thus, the motor M2 under the idle operating conditions, tends to hold back and oppose the normal driving action of i the motor -Ml so that the motor MI during idle feeding must ,overcome both the frictional force F and the opposing force of the motor M2.

The maintenance of this opposition by the mo- 'tor M2 under idling conditions is particularly significant in down-cut milling operations so that as the work approaches the cutter inidle feed- 4 1 ing movement and initially engages the cutter there will already be established an opposing effect instantly responsive to the hooking in or negative work resistance which results during down-cut milling and to thereby arrest and instantly neutralize the irregular motion which might otherwise result in the work table at the incipient stage of cutter engagement. 1

Considering the conditions where the down-cut milling operation is begun and continued, and referring to the elementary diagram illustrating this operating condition at D in Figure l, as the work table feeds along, for example, in the direction 28 with the same elementary circuit arrangement as set forth above, the cutter C begins to engage the work piece W and tends to pull the work piece along in the direction of the feeding motion so'as to assist or accelerate the normal feeding motion. As this takes place, the negative work resistance at first may build up to a point sufficient to equal the positive frictional force of the feed transmission and work table so that the two motors MI and M2 ultimately have their pressures changed to the condition as shown by the broken line I9 in Figure 1. At this point the negative work resistance and the positive frictional resistance balance each other and both of the motors have their pressures changed so that the pressure at the inlet port I5 of the motor Ml equals the discharge pressure at the outlet port 18 of the motor M2, and the pressure at the inlet port I! of the motor M2 is equal to the pressure at the discharge port l6 of the motor Ml so that these motors are balanced. This theoretical condition may temporarily exist where both motors exactly balance each other and wherein no effort is required to effect the feeding movement.

As the conditions indicated at line l9, Figure 1, are passed, the motor M2 now becomes a dominant motor to oppos negative work resistance during downcut milling as the motor Ml decreases its effective force exerted in the direction of feeding. This can be clearly seen on the diagram, and is indicated at 26 which is the changeover point for the motor Ml from applying a force in the direction of feeding to acting as an opposing member to the negative work resistance being developed by the down-cut milling operation. Thus, after the point 26 is reached and passed, both of the motors MI and M2 act as opposing devices, i. e., they oppose the feeding motion being effected by the down-cut milling operation, the motor M2 being the dominant opposing device at this time.

It is to be noted that during the down-cut milling action the pressures at the various ports of the motors MI and M2 are indicated on the diagram, Figure 1, between the lines 20 and 21. During relatively light down-cut milling, the motor Ml at all times acts in the direction of feed, though at a lesser value than the opposing action of the motor M2, so as to positively control the table movement against undesirable jumping motion. It is to be further noted that upon increasing the down-cut milling action to heavy cutting conditions, both motors will then automatically become opposing devices to properly maintain smooth movement of the work table in the feedgreases,qoressm'etbuildsrupnt'the intakeportrlisof the motor MI and decreases at the discharge port iii :of :this imotor. Durin zrelativelyilight iup lcut milling =thezmt0r 'MZ automatically tregulated byitheiinterconnectedmesistancesiR. I andI-R;2cconnected "to :the .motor Ml "as descflbeflsso that the pressure atthe discharge pbrtlw of theimotor M2 is somewhat higher than the pressure at the in- 113 1562110113 .I'! of this ".motor M2. Thus, there :is zmaintainedassmallopposing pressure by-the mostorm/l2 in :addition to the friction force? which must benverc'ome by'themOtQrMI *during light iupeElltTIIIflliIlETOPGI'ZfiORS. fIlhis opposition byzthe motor M2 under. light upcutmillingioperations is desirabl tormaintain rigid control of the work stable and prevent :any jumping action due sto'the lli'ght cutting forces and to ithefvariation in:.friction of the transmission :and :slideways 'Jfor the ibable.

..-As soonas excessively heavycutting beginsto .take place in the up-cut milling operation,ihow- :ever, both motors automatically :become {effective toadrive the work table in vthe fdirection:of z 'feeding movement. This is accomplished by the auto:

matictregulationofthe'resistancesxRl and'ERTso @that'when the 'point :23 *is reached the :motor M2 changes-over from anxopposing ideviceto a device lto 'assist'the motor 1M=l 'inzdriving thewo'rk table in feeding :direction. *It is to be noted that the smotorrM2 increases its assistance tothe'motor MI :as the positive work resistance during up-cut :milling increases. It will "be .noted that under :theserlatter 'circumstances' after the point :23 has been reached and passed that the motor M! :maintains the dominant driving action assisted to 'a lesser degree 'by "the 111101301 3M2 during the normal .up-cut feeding operations. Under these Hatter conditions the pressures 'Pl "and P2 at the arespective intake ports 45 and l or themdtors Ml and M2 .are maintained in excess of 'their respective output pressures BI and B2 atatherressp'ective discharge ports Band 13 of 'ithesefrnotor's *under the :ahove-recited conditions fOf (operation.

Summarizing the above operating conditions: when-the worktableis ibemgied'in idle motion with no cutting action taking-place between work r'and tool, the .motor M-l provides a dominant :motive force for "effecting the deed movement "which is opposed simultaneously-ibytheifriction forces :of the feed transmission and work table slide and by a small opposing force applied by the motor .M2. .As a negative -work resistance develops during down-cut milling :thetm'otor1vlf1 automatically increases its opposition "to the negative work resistance 'while the unotcr :Mzl

automatically decreasesits forwardieedin'giforne. This action :continues until the negative "work resistance of the down-cut milling 'inci eases nntil .the smotor Ml automatically changes :over :to assist the motor M2 in opposing "themovement of the work table in the feed direction.

During up -cut milling, as the table :passes from an idle feeding condition to an factive cutting condition, the motor .M'l tincreas'es effective Iiorce to move the table in feeding i direction while vinstan'tly:resporxslve:tomapidlyvaryingtforcesiincited by the cutting action of workianditoolwhich tend *to el-range the *desired smooth *operating movementof the work table. This arrangement automatically eliminates the backlash'in the mechanical interconnecting transmissions ibetween the-motors andithe'worktable and-therebyelimh nates Fall \chatter :and vibration which might Totherwise develop therein during the cutting operation. .-Also, this :s-ystem ;provides an arrangement whereby the motors are instantly sensitive to and adapted tozimmediately neutral riaerany variations in the "table movement during :theacutting operation. :Any' changes in thezforces 'appliedtbetween work and itool and rapid changes dirom both =up-cut :an'd down-font unning .to :idle sfeedin imotion :may rapidly =.take zplac'e with the motors MI and M2 instantly responsive te-such chan'ges.

:Inthe elementary descriptionrof this invention, as illustrated in Figure :1, there :has been shown .the instance 'of feeding in v one direction .28 only. This/invention is well adapted, however, to icedingrinboth directions and reference is had to the exemplary circuit shown \in Figure2. In this arrangementfeedingmotion-may readily takeplace not only in'the direction 28 but also in the opposite direction 3-2 so that both down-cut and upcut milling may be readily undertaken -in either of these directions.

in this embodiment operating fluid is derived i-rom .a fluid.reservoir 33 through the suction line 34 connected to the intake of the .gearpum-por rapid traverse .pump .35 which discharges fluid .underpressure tothe .pressure lineiifi. This line is connected toa selector valve 31 for controlling the ieedand rapid traverse movements of the work table T in either direction. The selector valve 31 has a suitable control lever -38 operable -to a feedleftposition 387), and a rapid traverse left position- 38c,.and also operable to a 'feed right position 38d, and a rapid traverse right position 38e. A .stop valve 43 having .a control lever 44 .movable ltova run position Maand a stop position 441) is provided to arrest movement of the work table. When the table is stopped, fluid pressure fromtheline-BG is connected through the selector valve 31 to a line 39 which is connected to low pressure :relief valve 40, which discharges into the drain line M .for :return of fluid to the reservoir 33. Under these conditions the rapid traverse, pump 351s thuscirculating'fiuid under relativelylow pressure through the lowpressure relief valve-40.

When the control-lever is moved to the rapid traverse leftposition 38c fiuid pressure from the :line :36 is then connected through the selector valve to the line 42 connected to the stop valve 43.. When the .control lever 44 of the stop valve is in'the :run sposition 44a fluid from the line 42 will lee-delivered to the-line-45-whichis connected "to the port l5 cf the :motor Ml. Return fluid .itrom theport IG-of thezmotor M4 passes through 'theline 4:6, thestop valve 43, the line 4-1,:selector valve :into the line -39 connected to the low pressure :relief valve and then into the drain .line 41 for return of :fiuid to the reservoir 33. It is to be noted that at this time fluid pressure the line 36 v"is not connected to the line .3 9 and :the llowpressure .relief valve 40 but is'corr- .finedz-in-theline 36 to which is connected-a higher ;pressure relief valved-8 which exhausts into the drain line M. This .;hieh'er :pressure relief valve its esta-blislies, anteater pressure in the :line 35 for proper operation of the motor M| at rapid traverse movements. r

When the control lever 38 of the selector valve 31 is moved to the rapid traverse right position 38c pressure from the line 36 will then be connected through the selector valve 31 to the line 41 and then through the stop valve '43 to the line 46 connected to the port I6 of the motor Ml. Return fluid from the port of the motor Ml will pass out through the line 45, stop valve 43, line 42, and the selector valve 31 to the line 39 and then through the low pressure relief valve 40 to the drain line 4|. The stop valve 43 may be operated by positioning this lever 44 in the stop position 44b to thereby simultaneously close off both of the lines 45 and 46 of the motor Ml to prevent its rotation and stop movement of the work table T.

Feeding motion of the work table T is effected by means of 'a locked hydraulic feeding circuit operating in conjunction with motor Ml which comprises a variable delivery high pressure feed ing pump l4 having a pressure delivery port 30 connected to the main feed pressure line 49 which is connected to the selector valve 31. The return line 58 from the selector valve 31 is connected to the intake port 29 of the variable delivery pump |4.' Both of the lines 49 and 50 are supplied initially with fluid from the rapid traverse pump pressure line 36 through the respective check valves 5| and 52. The feed pressure line 49 is maintained properly charged with fluid at all times by means of the high pressure booster pump 53 which is supplied with fluid from the branch line 54 of the pressure line 36 from the rapid traverse pump 35 and transmits the fluid under high pressure through the line 55 into the pressure line 49 of the circuit associated with the variable delivery pump l4.

When the control lever 38 of the selector valve 31 is moved to a feed left position 38b high pressurefluid from the line 49 is connected through the line 42, stop valve 43, to the line 45 connected to the port l5 of the motor M. Discharge from the port |6 of the motor MI at this time passes through the line 46, stop valve 43, and the line 41 to the selector valve 31 where it is then connected to the intake line 59 of the variable delivery pump l4 so as to provide a locked or closed hydraulic feeding circuit between the variable delivery pump l4 and the motor Ml.

A conventional differential relief valve 56 is employed which permits a complementary rise and fall in both forward and back pressure in the lines 45 and 46 for either direction of feeding so that the sum of the forward and back pressures in these lines must remain constant for any pressure difference which may exist between them. This valve has a pressure chamber 51 suitably connected to the line 49. Fluid may escape from the chamber 51 into the drain line 58 past the end of a spring-urged plunger 59 which is moved by a compression spring 60 in opposition to the pressure in chamber 51. A fluid pressure chamber 6| also acting in opposition to the spring 66 is connected through a resistance 62 to the return line 50 of the variable delivery pump l4. Pressure changes in both of the lines 49 and 50 reacting against the spring 68 effects the complementary pressure rise and mum the supply lines 45 and 46 for the motor MI in acreference may be had for a further detaileddescription of the operation of the differential relief valve.

. In order to best understand the operation of the motor M2 in conjunction with the motor MI in providing backlash vibration dampening action for the table T a typical operating cycle will be described. Assuming a work piece W to be properly mounted on the work table T, and the stop valve in a running position, the operator moves: the control lever 38 to a rapid traverse left position for rapid movement of the table in a direction 28 to bring the work initially into cutting position with the tool. As described in connection with Figure 1, both of the motors MI and M2 are mechanically connected to the common rack so that rapid movement of the table by the rapid rotation of the motor MI would cause rapid rotation of motor M2.

In order to effect rapid traverse movement without hindrance from the motor M2, means are provided for automatically cutting out or short circuiting the fluid circulation by this motor in the lines 63 and 64 through resistances RI and R2 interconnected between the ports l1 and I8 of the motor M2. This is accomplished by means of a short circuit valve 65 having a plunger 66 mounted for axial movement in the valve 65 and held in one direction by means of a compression spring 61 and adapted to be moved in the opposite direction by means of pressure applied in pressure chamber 68 provided in the valve behind the plunger 66. The pressure chamber 68 is'connected by a suitable line 69 to the feed range selector valve 10, having a control lever 1| movable to a low position 1|a and to a high position Hi). When the control lever 1| is in the low position 1|a, the line 69 is connected through .the annular groove 12 formed in the valve plunger 13 of the valve 10 to the line 14 connected to the line 54 which, in turn, is connected to the supply line 36 from the rapid traverse pump 35. A branch line 15 supplied through a check valve 16 from the line 14 serves to supply fluid from the rapid traverse pump 35 to the line 63 to at all times keep the circuit associated .with the motor M2 charged with fluid.

When the control lever of selector valve 31 is moved to the position 380 for rapid traversing movementto the left the pressure in the gear pump line 36 rises as above described since now the higher pressure relief valve 48 is operative while-the lower pressure relief valve 46 is disconnected from this line by the selector valve. The rise in pressure in line 36 causes a similar rise in pressure in the lines 54, 14, and 69 and likewise in the pressure chamber 68 of the short circuiting valve 65 so as to axially move its plunger 66-to overcome the spring 61 to interconnect the lines 63 and 64 through the annular groove 11. Thus rotation of the motor M2 at rapid traverse rates is readily permitted since fluid may freely circulate through the motor M2, the line 63, annular groove 11, and the line 64. This condition, of course, obtains as well when the control lever 38 of the selector valve is moved to rapid traverse right position 38c in which the fluid circulation by the motor M2 through the valve 65 would take place in the opposite direction.

Having thus positioned the work and table in initial cutting position, the selector valve is now moved'to a feed left position 3% which automatically reconnects the rapid traverse pump 35 through the-low pressure relief valve 40 thus reducing the pressure in the lines 54, 14, and 69 9a to cause the pressure to dropinthe chamber 6B of the short circu-itingvalve" to permit its spring 61 to axially shift the plunger to the-position shownin Figure 2. Feeding motiorrof the'table T takes place with high pressure fromthe line 49- delivered through; line 45 to the port ii of the motor MI and exhausted out through the port Iii-back throughtt; 41, 50, to the intake port 29- ofthe pump I4 as described: Pressure built up-inthe line 4-5 is transmitted through a line 45a connected through a resistance 18 into a pressure chamber 19' ofthevalve R-I caus ingpressure to build up behind the plunger- 80 to move it against-the compression spring 81- and thusmovethedouble tapered throttle spool 45b to connect line 45a toline 63a. The extent of movement of the' valve; spool lihwill determine the-pressure drop in*line 6312; with respect to the pressure line 45a;

Thepressure in line fific will be communicated through resistance '94 to. chamber'BS to exert,- in" conjunction withthe spring 8|, a counterbalancin'g force againstthe pressure in chamber 19. It will be apparent that the spring B'Fwill determine the amount-of the pressuredrop: The motors MI. and M2are geared together-in such a,way thatthey both displacethe'same volume offiuidas the table-travels-in feeding movement, so that theamount' offluid passing through one motor will be equai to, the. volume of fluid'passing through the other:

Thefluid' discharged from motor M2'will pass into line 6 lwand'iwhen the, pressure in that line has risen: sufiicientl'y. it. will" react in chamber 81 and cause shifting of plunger 88 and its double tapered" valve spool 46b to' open port 460. The pressure necessary. to open this port is determined by spring; 82fandmust obviously be higher than the pressure-in line 460; or in other words the discharge pressure. from the first motor; In this way, the pressure drop across the. second motor is'maintained' less than thepressure drop across the first motor during up-cut milling operation.

When-the table is moving in direction-32with the forward pressure of the pump acting through 45 to motor MI and through resistance valve 89 to- 63a,63and motor M2; the back pressure of motor M2 iscommunicated through St -54a to the pump back pressure Mia-46 through throttle valve 88. For any given feed rate throttlevalves 80 and 88will have established a position to-give a constant pressure drop fromlines45a to 63a and from lines tfiazto 64a respectively. The differential relief valve 59 will-have established the position to give the proper pressure valuesfor v the load as shown in-Figure 1. If a large transient impulse load is suddenly encounterednone-of these valves will move because of the damping effect of the choke coils on these valves.- If, for instance, the-table should tend toaccelerate in thedirection of the feed as in down cut, theoil in the back pressure lines Miand 64v will tend-to compress because the motors would then acceler ate through the rack- [2. This causes a rise in pressure in these lines because the fluid has no- Whereto go momentarily. The reverse-happens on the forward pressure lines 45 and 63. The oil in these lines tendsto expand under the rapid acceleration. Therefore, the eiiect is. two-fold: a lowering of the forward pressure momentarily and a rise in theback pressure momentarily, which in'the systemshown issufiicientito minimizemovement to a-very smallzvalue, .thusieffecte ing substantially smooth tableoperation.

Withtheamotors workingunder load duringlan up-cutmillingoperation; a sudden rise in work resistance will react toi'ncrease'the pressure in the supply lines 45', 45a--6-3,'and decrease that in lines 64a--4f6a, increasing the pressure drop across the motorMZ so that this motor will exert more driving; power to overcome the increase in load: Thus, during upecut milling, asthe-load on motor M-I- increases, the motor- M2= is caused to tendergre'ater andgreaterassistance to the motor MI in overcoming the increased-resistance.

In down-cut milling, the cutting; force maybe sufii'cientto act as the drivingpower forthe table and the motors function tohold-back the table. With the locked circuit" as explained, the pressure in line 4t of the=fiuid discharging fronr the motor Mi willbe higher than the pressure in line 45 A similar-effect Wouldjbe produced in the lines 63a" and 6th or motor M2, the pressure'in line Ma'being higher-thanthe pressure'in line=63a-.

The purpose of the fluidresistances, or choke coils. 1 8* and 9t; and stand 86 associated with the respective variable'resistance valves R; landRi2,'. is to, restrict too rapid a response and excessive hunting of. the valve plungers 8'0 and 83 during the operation offthedevice" to thereby providea smootheven/control" for the work table;

The-linettw isconnected-tb" the short circuit; ing' valve-"65 whichat this" time connects fluid from the finesse-through the'anrrulargrcove I! of its-plunger 66* tor the-liner63=connected to the port of the motor'M-2'i this port being an. inlet port; when feeding, inthe-direction 28' to the left. Discharge from' the" port It of the" motor at this time passes through the line 64' and theian nular groove 84 of the valve plunger fit-intothe line; 641v and through, a' resistance 88 connected to the pressure: chamber 8'1" of the" twot-way resistance valve R2; Asithe" pressure builds up in the"chambert'ltheplunger88 ofthe valveRZ is moved axially-compressingthespring 82. so as to. connectlinet itz t'o' the line llia'whicl'i in turn is connectedftothe 1111646. and'the port I 6 'ofth'e motorMl. At the: conclusion of'the feeding motion ihthe direction 28 t the lever 38" of the selector valve is moved" to' rapid traverse position: 3'8e' for return r'apidtraverse movement to the direction 32. As described; rapidtraverse pressure from-1 line 36 is'then connectedto the'portlfi'ofthe motor M1 while themotor M2 is.short circuited by theivalve 6 5: for free rotation during rapid movement of the abl' T 1 Feed in. the direction 32 may. tlienbe. effected by, positioning the. controlilever 381 of the, selector valve .31; inLthefeedlri'glit'. position .3862. Feeding. pressure. will; then. beapplied atthe port. [61 of the. motor. Ml, while. lower pressurewill. be res turned from v.the porttlipbackmo. the, variable .de.- livery pump lAv. Under. these conditions pres.- sure will be transmitted out through the: line. 46a front-the line. 46 through .resistance -8 3. .to thepressure-chamber '9 2".of the'valve, R2. which will cause the-.plungen88 to shift axially, compressing spring 9 3 and .openi-ng line; 46a to 5 communication with line S im-to. :cause'aipressure :drop :in dinet imwith respect to lineulfia. Eluid mayi then pass-through the:annular. gro0ves84zof= they-plunger) 616 of. the shortzcircu-iting va'lve tfirl-intmthe line 6t and :thus intothe 1 port 1 lflrofiathegmotortm-zi. Discharge. from ports] l of; this :motor-.:then :piasses out through the line; 6 3; annular groove= lih of; the 1 valve: plunger 66 to::.thei:line fifia-rthen 1. through the resistance 941i into:thecpressureichaanber:8950f the; valvez-R'l; to: move tliecplungerrflll against: the? compression springellll tmcomlectttheclinezfitrrmithothe:line245m causing a pressure drop in line 45a with respect to line 63a. The line 45a is connected to the line 45 and the port I associated with the motor Ml. Thus the two-way resistance valves RI and R2 are arranged to automatically function for either direction of feeding movement to provide the desired pressure drop as shown in Figure 1, between the ports l5 and I1, and I8 and N5 of the motors MI and M2 by the relative position of their central plunger spools 45b and 46b with respect to the ports 45c and 460, the plunger being actuated by pressure changes created in the lines connected to the ports of the motors MI and M2 by the reaction of work and cutter. The various pressures resulting during the feeding motion in either direction has already been described in connection with Figure 1 except that when feeding to the right the pressures PI and P2 would be opposite to those of BI and B2 in the diagram, Figure 1.

When it is desired to effect a relatively high rate of feed for the work table, the control lever H of the feed range valve 10 is moved to the high position 1 lb so that high pressure from the feed supply line 49 is transmitted through the line 95 and the annular groove 12 of the plunger 13 to the line 69 to thus provide a high pressure in the chamber 68 of the short circuiting valve 65 suflicient to cause the plunger 66 to compress the spring 61 and interconnect the lines 63 and 64 of the motor through annular groove 11 to thereby allow free rotation of the motor M2 during movement of the work table at rapid or high rates of feed.

What is claimed is:

1. In a machine tool having a movable member subject to variable resistance forces tending to modify the movement of said member, an actuating device for maintaining uniform movement in said member comprising, a pair of hydraulic motors mechanically connected to drive said member, a fluid pressure pump, a hydraulic impelling pressure circuit including conduit means interconnecting said pump and one of said motors, a return pressure conduit for said motor and means for connecting the other of said motors to the hydraulic impelling pressure circuit and the return pressure conduit in parallel with said first motor through a pair of fluid resistances.

2. In a machine tool having an actuable member movable relative to a cutting tool, an actuator for said member including the combination of a pair of hydraulic motors, each mechanically connected to drive said member, a fluid pressure pump, a locked hydraulic feeding circuit interconnected between said pump and the intake and exhaust ports of one of said motors, and means coupling each of said ports of the one motor through fluid resistances to corresponding ports of said other motor.

3. In a machine tool actuating mechanism for a movable machine member, a first hydraulic motor connected to actuate said member in aselected direction, a fluid pressure pump, a locked hydraulic feeding circuit interconnecting said pump and the intake and exhaust ports of said motor, a second hydraulic motor connected to actuate said member in the same selected direction, a fluid resistance interconnected between the intake ports of said motors and a fluid resistance interconnected between the exhaust ports of said motors whereby the pressure at the intake port of said second-mentioned motor will be lower than the pressure at thev intake port of said first-mentioned motor and wherein the pressure at the exhaust port of said first-mentioned motor will be lower than the pressure at the exhaust port of said second motor.

4. In a machine tool having a work table movable relative to a cutting tool to effect a cutting operation on a work piece mounted on the table, an actuating mechanism for effecting said relative movement comprising a main fluid pressure motor mechanically connected to drive said work table, a fluid pressure pump connected by a locked hydraulic feeding circuit to the intake and exhaust ports of said motor, whereby the cutting action between work piece and cutter tends to retard or accelerate said motor to effect complementary pressure rise and fall between the ports of said motor, a second fluid pressure motor mechanically connected in driving relationship with said first-mentioned motor and said table, and means for connecting the inlet and exhaust ports of said second-mentioned motor through a fluid resistance to the corresponding ports of said main motor whereby changes in pressure at the ports of said main motor changes the torque characteristics of said second-mentioned motor to neutralize variations in said table movement in response to work resistance changes taking place between the work piece and cutter.

5. In a milling machine having a relatively movable work table and a cutting tool adapted to effect a cutting operation on a work piece on said work table, an actuating device for effecting said relative movement including the combination of a main fluid pressure motor mechanically connected to said table, a fluid pressure pump connected by means of a locked hydraulic circuit to said motor, and a second fluid pressure motor mechanically connected to said table and hydraulically connected in parallel with said firstmentioned motor through a pair of resistances respectively connected between the intake and exhaust ports of said motors whereby said second-mentioned motor neutralizes irregular movements in said work table.

6. In a machine tool having a work table movable relative to a rotary cutting tool and an actuating means for said table effective for either direction of feed of said table and rotation of said cutter to effect uniform feeding movements in said table, the combination of a pair of hydraulic motors, mechanical driving means interconnecting said motors and said table, a fluid pressure pump, a locked hydraulic feeding cirneutralize the effect of variation in cutting forces applied to said table by action of said tool on a work piece on said work table.

'7. In a milling machine hydraulic feed transmission adapted to actuate a work table, a hydraulic motor, a mechanical drive connecting said motor to said table, a fluid pressure feeding pump, a locked hydraulic circuit interconnecting said pump with said motor, a second hydraulic motor, mechanical driving means connecting said motor to said first-mentioned motor.

and to said table, adjustable fluid resistances connected between the intake and exhaust ports arrears.

of. said motors, and means;.operated byfluid pressure changes insaid locked hydraulicfeeds ingscircuit for adjusting said resistances to. vary ble, a source of rapid traverse flui ressure con nectable to said motor, a source of feeding pressure connectable to said motor, a selector valve for operatively connecting one or the other of said sources to said motor, means for changing the rate of feed to said hydraulic motor, a backlash control motor hydraulically interconnected through resistance means with said first-mentioned motor effective during low feed ranges to restrict movement of said work table, a control valve, associated with said backlash motoroperabjle to, short circuit. said motor to render- ,it ineffective to restrict movement, of said, table when operating in high feed ranges, amil means, operable by the positioning of said selector valve to effect rapid traverse actuation of said firstmentioned motor to operate said control valve to render said second-mentioned motor ineffective to restrict movement of said work table.

9. In a hydraulic mechanism, a work table, a first hydraulic motor mechanically connected to drive said work table, a variable delivery high pressure feed pump including means adjustable for efiecting high and low feed ranges, a locked hydraulic feeding circuit interconnecting said pump and said first motor, a rapid traverse supply pump for said circuit for actuating said motor in rapid traverse movements, a selector valve operable to render said feed or rapid traverse pumps effective to actuate said motor, a second motor hydraulically connected through resistance means across the ports of said first motor, a feed range selector valve operable to a low or high range position and efiective when in said high range position to cause said second motor to be rendered ineffective.

10. In a hydraulic mechanism, a work table, a first hydraulic motor mechanically connected to drive said work table, a variable delivery high pressure feed pump adjustable for high and low feed ranges, a hydraulic feeding circuit interconnecting said pump and said first motor, a a

rapid traverse supply pump for said circuit for actuating said motor in rapid traverse movements, a selector valve operable to render said feed or rapid traverse pumps effective to actuate said motor, a second motor hydraulically shunted through resistance means across the ports of said first motor, fluid pressure control means including a feed range selector valve operable to a low or high range position effective when in said'high range position to cause said second motor to be rendered inoperative, and means whereby the positioning of said selector valve to operatively connect said rapid traverse pump to said first motor automatically actuates said fluid pressure control means to render said second-mentioned motor ineffective to restrict motion in said table.

11. In a hydraulic feed transmission for a work table, a main hydraulic feed motor mechanically connected to drive said table, a hydraulic feeding circuit associated with said motor including means for applying a variable feeding volume and a rapid traverse volume to said motor, a selector valve in said circuit for rendering said feed or rapid traverse volumes operative on said motor, a. second motor mechanically connected inldriuing relationshipwith said; tableand; said first-mentioned. motor, a fluid pressure. control circuit includin resistance means. interconnected with said circuit effective to cause said;

second-mentioned motor to apply variable, forces to said. tabl accordance with cha es in. the work resistance applied said ta le. fluid floweon r 1=- m ans f r r nd r ng said; s cond motor inedective whe high rates of. eed n ar e n effect d saidfirst-m nti ned motor, and;

further contro meansv nerableb the moverm ntv f: said elector-valve tQoperativdy onne tsa d rapid raverse vo ume oo-sa d: first-ment n .m.Q-- tor to autom t ally ender said secondemene tioned motera n fec ve s 1.2-. A h d a li fe di me han m f r a ma.- hin tool membe comp is n a, pair of hY- ra ic m s havi g; their n a e. ports. inter. connected throu h. a fluid esistance-a d their ax h t ports in rconnected through anoth r f u d.- resistanc a fluid pres ure pump. h in ts in; take and exhaust ports directly connected respectively to the exhaust and intake ports of one of said motors and by way of the fluid resistances to the respective ports of the other motor, and a common mechanical driving connection between said member and both of said motors.

13. In a milling machine hydraulic feeding mechanism for actuating a work table, the combination of a pair of hydraulic motors connected through a common mechanical driving connection to said work table, a source of fluid pressure for actuating said motors at low and high feed rates and at a rapid traverse rate, control means for rendering said rates selectively effec tive, means for automatically rendering one of said motors inoperative when high feed rates are being effected in the Work table, and further means for automatically rendering said one motor inoperative when said table is operating at a rapid traverse rate.

14. In a hydraulic feeding mechanism for a milling machine work table, the combination of a main hydraulic actuating motor, a hydraulic backlash control motor, mechanical driving means interconnecting both of said motors to said work table, a fluid pressure circuit connected to said first motor, a, source of rapid traverse pressure and a source of variable feeding pressure, selector valve means for connecting one or the other of said sources of pressure to said circuit, a control circuit associated with said second motor, and control valve means in said circuit operable from said source of rapid traverse pressure to render said backlash control motor inoperative when rapid traverse pressure is applied to said main actuating motor.

15. In a hydraulic feeding mechanism for a milling machine work table, the combination of a main hydraulic actuating motor, a hydraulic backlash control motor, common mechanical driving means interconnecting both of said motors to said work table, fluid pressure circuit connected to said first motor, a source of rapid traverse pressure and a source of variable feeding pressure, selector valve means for connecting one or the other of said sources of pressure to said circuit, a control circuit associated with said second motor, control valve means in said circuit operable from said source of rapid traverse pressure to render said backlash control motor inoperative when rapid traverse pressure is applied to said main actuating motor, and manually actuable control valve means operable in accordance 15 with tire" rate 6! feed to be effected in said firstmentioned motor to automatically operate said first-mentioned control valve means for said second-mentioned motor to render said second motor inoperative when high feeding rates are being effected in said Work table.

16. In a hydraulic transmission organization for actuating a milling machine work table, the combination of a source of rapid traverse pressure, a source of low and high feed pressure an actuating motor, a hydraulic circuit connected to said motor and to said sources of pressure, control valve means in said circuit for selectively applying one or the other of said sources of pressure to said actuating motor, a second motor mechanically connected to said first-mentioned motor and to said work table, a control circuit associated with said second motor and interconnected through resistance means to said circuit associated with said actuating motor, control valve means in said control circuit automatically operable by the source of rapid traverse pressure during rapid traverse movement of said work table to render said second motor inoperative and selector valve control means in said control circuit for transferring control ofsaid control valve means fromthe source of rapid traverse pres sure to the source of feeding pressure whereby said second-mentioned motor is automatically rendered inoperative during relatively high rates of feeding motion of said work table.

HANS ERNST. ALBERT DALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,236,256 Allard Mar. 25, 1941 2,309,637 Fickett et a1 Feb. 2, 1943 2,493,512 Vickers Jan. 3, 1950 

